Resolution with APS sensor vs. full-frame

Discussion in 'Digital Cameras' started by Paul Flackett, Sep 25, 2005.

  1. I'm having difficulty getting my head around the variables with DSLR's.
    Would I be correct in thinking that an 8MP APS sensor camera like the
    EOS 20D would be just as good for the bird photographer as the 5D
    (costing considerably more) with the same lens when the image from the
    latter is cropped to the same area as that captured by the former? Or is
    it not quite as simple as that - is the resolution better by default
    with a full-frame sensor?

    I've always considered the 1.5 factor to be a real advantage with my 20D
    allowing me to get more magnification for my money. What would I be
    gaining by upgrading to the 5D?
    Paul Flackett, Sep 25, 2005
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  2. For the bird photographer, the 64-dollar question is how well does the
    (slightly) improved AF tracking (with the 6 extra sensors) work with a 1.4x
    TC as opposed to the 20D's AF without the TC.
    (1) 25% better linear resolution (using lenses with the same FOV)
    (2) Lower noise (should be noticeable at ISO 800 and above)
    (3) Better dynamic range (should be noticeable at ISO 100)
    (4) Spot meter
    (5) Interchangeable focusing screens
    (6) Ability to get a 12mm FOV with the Sigma 12-24.
    (7) Fisheye
    (8) The 24mm TSE acts like a 24mm TSE instead of a 38mm TSE

    Note that all of these are enormous for landscape photographers, not bird

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Sep 26, 2005
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  3. Paul Flackett

    Bill Guest

    It's not as simple as that.

    There are advantages to both imaging sensors, and it depends a lot on
    what you want to accomplish. But comparing the 20D and 5D imaging
    sensors, you will find the 5D has a larger "receiving area", which
    should translate into less noise and a brighter image with the same
    lense and same conditions.
    This is a common misconception - it's a crop factor, not any kind of

    Putting a 200mm lense on a 20D does _NOT_ get you any closer to the
    subject than using the same 200mm lense on a full frame camera.

    A 200mm lense is a 200mm lense, on a full frame and a 1.6x body. The
    difference is _ONLY_ the field of view, or how wide the final image will
    appear and how much scenery will be visible around the subject.

    To see an example image of what this means, scroll about a quarter of
    the way down the following page:

    Further down, another example shows the difference between full frame
    and 1.6x crop with a 400mm lense and how the zoomed size appears larger.
    Lots of things related to features and performance, and slightly better
    image quality.

    I think the biggest advantage would be the full frame sensor that allows
    you to use a 28mm lense as it was intended. For wildlife photography,
    it's not a major factor.
    Bill, Sep 26, 2005
  4. Paul Flackett

    Stacey Guest

    Bill wrote:

    Actually it changes the FOV which is what also happens when you use a higher
    magnification lens. Why people are so hung up on relating everything to
    35mm full frame mm of focal length is something I'll never understand. Or
    why this "It's works like that mm of lens is suposed to". Focal length and
    FOV changes with format whether it's 6X9, 4X5, 4/3 or APS.

    FOV is all that really matters. A 90mm lens is a nice wide lens on a 4X5,
    should I be upset and demand that any camera should have a wide FOV with a
    90mm lens? Of course not, that would be a silly arguement.
    In real use it does. A 200mm lens is a wide angle lens on an 8X10 camera,
    doesn't mean it's still a wide angle lens used on a 20D.

    Using the same 200mm lens on a 20D will get you closer than that same lens
    used on a 35mm camera or a 5D, unless you crop the image of course. Then
    you have less MP so it's doubtful the image quality would be as good. And
    why pay $3500 to "upgrade" if your going to end up cropping to a smaller MP
    final image?
    Which is all that matters, the mm of the lens is a meaningless number. FOV
    is all anyone should care about, period! Why people rant about this "A
    200mm lens is a 200mm lens" is absurd. From what you're saying, there is no
    difference between


    except the first has an angle of view of 55 deg and the second of 12 degree
    like that's of no real concern to the end user and we should be FOCUSED on
    the number of mm the focal length of the lens is..

    Not unless he buys new longer/larger/heavier/more expencive lenses so he has
    the same FOV across the whole sensor.
    Stacey, Sep 26, 2005
  5. Most people will only need one new lens, the longest one. All the others
    will work fine. Unless they bet on the wrong horse.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Sep 26, 2005
  6. Paul Flackett

    ASAAR Guest

    I think it would be more than a slight advantage, unless I'm
    making a calculation error somewhere. If the 20D's sensor was as
    large as the 5D's sensor it would have 6.2 x 1.6 x 1.6, or about
    15.9mp. So if the same focal length is used with both sensors, any
    subject's image that fits within both sensors (as would be the case
    where you can't get close enough to a bird to fill the frame), the
    image on the 5D's sensor would utilize 8.2 / 15.9, or 0.52 times the
    number of pixels. That is, the image in the 20D would contain
    nearly twice the number of pixels. The 5D would have the edge only
    if the bird was close enough so that the 20D would have to use a
    much shorter focal length than the 5D to keep the bird's image from
    exceeding the size of the sensor.
    ASAAR, Sep 26, 2005
  7. Paul Flackett

    Stacey Guest

    Which will also be the most expencive, heaviest, largest lens they've ever

    If they were using a 200mm f2.8 1.68 pound lens and liked this FOV on the

    They'd have to get at least a 300 f4 2.6 pound lens at twice the price and a
    full stop slower.

    If they want the same lens speed, add 4.5 pounds to the weight of the 200mm
    lens and about $3000 more bucks!

    Yea that's nothing for anyone to concern themselves with. Just plop down
    $3500 for the body upgrade and $3800 for a new lens to cover the same FOV
    at the same speed and haul around 5 -more- pounds of camera.
    Stacey, Sep 26, 2005
  8. Paul Flackett

    Stacey Guest

    ASAAR wrote:

    No way, the 5D RULES!!! Don't you know anything? :)
    Stacey, Sep 26, 2005
  9. Not quite - you are using the wrong resolution for the 5D, it has
    12.9Mp, not 8.2Mp.

    Cropped to the same focal plane area, the pixel resolution is simply the
    square of the pixel pitch. On the 20D that is 6.4um; on the 5D it is
    8.2um, so the 20D will have around 1.64x as many pixels in any given
    crop size, including the full APS crop of the 20D.

    However, pixel counts isn't everything - all pixels are not equal. Those
    smaller pixels demand more performance out of the optic to be properly
    resolved - same problem that besets P&S digital cameras, albeit on a
    different scale. Even with diffraction limited optic, for anything
    above f/11 the actual resolution of the image is determined by the lens
    not the 6.4um pixels. For 8.2um. that increases by over a stop. So if
    you are shooting at f/16 you won't really be getting 8Mp of information
    on the image with the 20D, more than 50% of it is superfluous redundant
    data. In addition to which, the larger pixels from the 5D *ought* to be
    (since they aren't in general supply yet that is an assumption) more
    sensitive and less noisy.

    Taking everything into account, what actually matters in these type of
    estimates is usually total focal plane area. How it is diced up into
    small noisy pixels or large sensitive ones is generally a second or
    third order effect as long as the pixel sizes being compared are within
    the useful range photographically.
    Kennedy McEwen, Sep 26, 2005
  10. That last point is key, yes. I finally invested in a new wide lens to
    extend my digital wide end to match what I had on film (Tokina
    12-24mm). Meanwhile, the much more expensive fast long lenses all get
    a little better :)
    David Dyer-Bennet, Sep 26, 2005
  11. Paul Flackett

    ASAAR Guest

    Thanks, I should have remembered that. I had a feeling that
    something would go wrong when I added "unless I'm making a
    calculation error somewhere", since at the time I could barely read
    the screen. Even now my eyes are nearly swollen shut due to some
    pollen allergy that started a little over a day ago. At least the
    headache/eye pressure is nearly gone. It would have been better if
    I'd have noticed microns != mega. :)

    As you noted, the 20D has 1.64 times the number of pixels for a
    given crop area, vs. my 1.94 (15.9/8.2) miscalculation. But that's
    still quite a large increase, very near to the difference in going
    from a 6mp to a 10mp sensor.

    I think you're going a little overboard here in trying to
    emphasize the superiority of FF sensors. The example under
    discussion was of using a long focal length to maximize the size of
    a bird's image. Do nature photographers often use apertures as
    small as f/16? I don't think they carry the excessive weight of a
    really good, large lens only to stop it down to a tiny aperture.
    And while as you say, the 5D ought to be less noisy, the difference
    in size between the 20D and 5D sensors is much less that the
    difference in size between notoriously noisy P&S sensors and the
    20D's sensor. So if the 5D is less noisy that the 20D, it probably
    won't be by nearly as large margin.

    This is true, but only if the total focal plane area can be used.
    As I said in my reply:
    If that wasn't completely clear, it implied that in such a case
    the 5D would be able to use the full frame (no cropping).

    But for this type of photography, often the full frame won't be
    able to be used, either because the bird is too small or too
    distant. When that's the case, the number of pixels used for the
    bird's image will quickly increase in the 20D's favor, reaching (as
    noted above) the same percentage difference as that between a 6mp
    and 10mp sensor. If cropping can be avoided though, the 5D would
    have a significant advantage.
    ASAAR, Sep 26, 2005
  12. Why thankee kindly Bill.And thanks everyone for your views. I think I'm going to have to stop
    worrying about whether I've bought the right equipment. I've been
    beating myself up for ages about about buying the Canon 400 f4 IS DO
    instead of the 500 f4 IS but then I just remind myself that it's about
    half the weight and I've probably taken it places hanging from my
    shoulder when I would have left the 500 at home.

    Not being a professional, (in fact I haven't made any money from
    photography at all yet) I can only afford one of everything!
    Paul Flackett, Sep 26, 2005
  13. Paul Flackett

    Skip M Guest

    Well, you pays yer money and you take yer choices, don't you?
    Skip M, Sep 27, 2005
  14. Paul Flackett

    ASAAR Guest

    And still much less than the difference multiple-stop difference
    between tiny P&S sensors and APS size sensors, as I said. If the 5D
    gets you about a one stop noise advantage over the 20D that's nice.
    And as I said, for many/most other situations it's a real advantage
    over the 20D's sensor. But in cases such as were under discussion
    where a particular image produced by one lens would utilize far
    fewer pixels with the 5D's sensor, the reduced resolution should be
    far more significant than a little extra noise.

    It appears to me that you're not disagreeing with what I've said
    (nor do I disagree with what you're saying) but you want to find
    ways to put the 5D's sensor in the best possible light.

    <pun intended>
    ASAAR, Sep 27, 2005
  15. Paul Flackett

    Stacey Guest

    Skip M wrote:

    Sure, just seems odd to blow off FOV like it's a non-issue or the "So you
    buy a huge 4X more money lens to get the same FOV" comments like it's not
    even a consideration.
    Stacey, Sep 28, 2005
  16. Paul Flackett

    Stacey Guest

    Sure he is. If what he posted was a fact, a 20D would have a massive
    performance disadvantage vs a 10D. For that matter canon should start
    making a 2MP FF sensors again to get giant pixels?

    Like I said "5D's rule no matter what!"
    Stacey, Sep 28, 2005
  17. Paul Flackett

    Stacey Guest

    That depends on whether you consider the 1 stop resolution advantage to
    be massive or not, doesn't it.[/QUOTE]

    1 stop resolution? I didn't realize resolution was measured in stops..
    Good grief.. Looks like the "full frame guys" are going to be quite
    irritating around here. So we go from trying to discuss if a cropped 5D
    shot would be lower resolution than a uncropped 20D one to this extream
    Stacey, Sep 29, 2005
  18. Paul Flackett

    Stacey Guest

    Assuming they already own one plus the APS lens isn't heavier or more
    expencive to the same FOV FF one.
    Stacey, Sep 29, 2005
  19. Paul Flackett

    W.E. O'Neil Guest

    No, I think he is right. For your lens array to cover the same effective FOV
    it did when you were shooting 35mm or 35mm sensor, you are going to have to
    buy one more wider lens to maintain the original widest FOV you had
    previously. Otherwise the crop sensor is limiting the capability you already
    had (assuming 35mm sensor or emulsion)

    Where he is wrong is that he doesn't consider the advantage that brings to
    the shooter 1) elimination of glass edges in the WA shot, 2) more effective
    reach at the other end of your lens array and 3) the shooter may have needed
    a new body plus more reach and decided to buy a camera that granted that
    extra reach without having to buy a new telephoto. So spending the extra
    money isn't only about maintaining similar capabilities, but also about
    improving overall quality and capability across the whole lens array.

    My primary reason for excluding any FF body is the edges of the glass in
    anything 24mm and wider. It has always been a prohibitive shortcoming in
    35mm shooting. It is even worse in FF sensors because at the top of the heap
    the sensors are so very good. My preference has been to add reach (without
    buying another lens) but to eliminate corners in WA while keeping the same
    FOV (by buying a wider lens in order to maintain my previous widest

    At the top of the dlsr market Canon and Nikon have very different ideas
    about sensors and imaging. In Nikon's case they have determined that
    eliminating the corners during the compositional stage is an advantage that
    some people will find worthwhile. I happen to be in that camp, and so am
    shooting a d2x. But I think people who don't shoot 24mm and wider with much
    frequency are going to be better of with a FF body like the 1ds mkII.

    Pixel count isn't as critical to me as it is to some because at the levels
    of 12 and 16 mp it is the software that becomes critical, not the difference
    in resolving power. I think the noise issue is way overstated as
    well.....but hey, this is a newsgroup!

    But of course that is all just my opinion :^)
    W.E. O'Neil, Sep 29, 2005
  20. Just as people with a lens collection they are happy with migrating from
    APS-C to full-frame will only have to buy one lens (or one 1.4x TC (see
    below)), folks migrating from a filled out 35mm lens collection in their
    film days will only have to buy one lens.

    Unless you bet on the completely wrong horse, changing horses in mid-stream
    isn't all that painful. But people who bet on the completely wrong horse are
    going to squawk loudly and obnoxiously about the more sensibly designed
    systems. They can be ignored.
    Uh, that doesn't work. Please, think. (a) Lenses get worse overall as they
    get wider and you have to use a "wider" lens on the small sensor (while some
    lenses really do collapse at the far corners (beyond 18mm from the axis),
    most wides get funky either over the whole field or gradualy). (b) You have
    to use more magnification to get to the print from the small sensor (this
    one's a double whammy, because the smaller sensor has a finer pixel pitch
    requiring more resolution: a 35mm lens has a lot easier time providing 40
    lp/mm (5D limiting practical resolution) than a 24mm lens does providing 53
    lp/mm (20D ditto)). (c) What makes wide lenses get funky at the edges is
    that it's hard to make wide lenses without getting funky edges, so you can't
    even redesign for the smaller sensor. (Although redesigning does have the
    advantage of a more modern design.)

    2) more effective reach at the other end of your lens array

    This one's also less than claimed: if a lens is adequately sharp on a 1.6x,
    it will be adequately sharp on a FF sensor _with a 1.4x TC_. The extra
    sensitivity of the sensor will also exactly make up for the lost speed.
    If you've already got FF, a TC's a better idea than a small sensor. Of
    As before, there's no such thing as a free lunch, and if you see a free
    lunch, you should be suspicious. The 'crop off the bad parts' argument reeks
    of free-lunch-itis. (Note also that decent telephotos have almost no edge
    funkiness to cut off.)

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Sep 29, 2005
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